Sharpening Lawnmowers

Any tool with a cutting edge,
whether old or new, must be sharp to perform satisfactorily. Mass-produced
items such as chisels, planes, knives, lawnmowers, etc., generally need
to be sharpened before use. Fortunately, there are devices and kits available
for sharpening these tools; however, the trick is to determine which one
is needed. Let's look at the requirements of lawnmowers.

What to use to sharpen your lawnmower blades
depends largely on the type of mower you have and the condition of its
blades. Most reel mowers, the ones that run on your energy, have five
blades that are twisted from one end to the other so at least two blades
are cutting at one time. Reel mowers can be sharpened with kits that contain
lapping compound or abrasive strips. Rotary mowers, the types that operate
on gas or electricity, can be sharpened with a grinding wheel, sanding
belt, stone or a file.

For
reel blades that are undamaged and just need their edges "refreshed"
to bring them back into perfect condition, a kit with lapping compound
is all you need. These easy-to-use kits usually include an application
brush and a crank handle.

Remove a wheel (it doesn't
matter which one) and the pinion gear, which is on the end of the reel
shaft. Mount the crank handle onto the reel shaft. Use the brush to apply
the abrasive compound along the entire length of each blade edge as well
as on the cutting edge of the bar that makes contact with the blades.
Turn the blades away from the cutting bar to sharpen them. You will hear
a gritty, grating sound and feel some resistance, but this is normal.
When the blades are sharp (after about 100 to 150 turns), you will feel
a fine wire edge forming on the front edge of the blades. You may need
to reapply the abrasive compound and repeat the sequence two or three
times. Remove the remaining compound by spraying the blades with water,
then wipe the blades dry.

To test blade sharpness, tear
some newspaper into 2" wide strips about 12" long. Turn the
crank so the blades come toward the cutting bar, and feed the newspaper
strips between the blades and the bar so the newspaper is cut off across
the 2" width. Each blade should cut the paper cleanly where it meets
the bar. If the newspaper folds over, the blade may need more sharpening
(check for burr on front of blade), or the cutting bar may just need to
be adjusted. Remove the crank handle and reinstall the pinion gear and
the wheel.

For
reel blades that are nicked or badly uneven, kits with abrasive strips
are your best alternative. Such kits come with a bar that holds an abrasive
strip. The bar clamps to the cutting bar and the abrasive sharpens the
blades at the correct angle as the blades are turned. To use this kind
of kit, adjust the cutting bar to allow enough room for the installation
of the bar with the abrasive strip on it. Position it on top of the cutting
bar and readjust the cutting bar so that the blade comes into contact
with the abrasive strip. Rotate the reel to sharpen the blade from one
end to the other, until each blade is shiny from the abrasive strip and
all nicks have been removed. Loosen the cutting bar, remove the bar with
the abrasive strip on it and readjust.

You
can sharpen the blade of a rotary mower on a bench grinder, belt sander/grinder
or with a rotary blade sharpener that fits in your drill. You could also
use a file. Before sharpening a rotary mower blade, disconnect the spark
plug wire on a gasoline engine or the power cord on an electric mower.
Remove the blade from the mower and remove the grass from the underside
of the mower as well as from the blade. Grind the bevel back until you
feel a burr develop on the back side. Remove the burr with a fine file,
keeping the bottom flat.

If you must put a small bevel on the bottom of the blade to repair some
damage, do it to both ends in order to keep the blade balanced (so your
mower doesn't get the shakes and wear out your crankshaft bearings and
your nerves). To check your blade's balance, put a narrow edge tool (such
as a putty knife) vertical in a vise, and set the mower blade on top at
the center point. If the blade consistently leans to one side, remove
more metal from that side (regrind that bevel). When the blade is balanced,
re-install it on the mower (with the bevel up and the flat side down),
set the mower upright, and reconnect the spark plug wire or extension
cord.

Resharpen your lawnmower blades
as frequently as your grass gives you signs that your mower blades are
getting dull. If the grass tips turn brown or the grass looks torn rather
than sheared, it's probably because your mower blades need to be resharpened.